2015-11-13 08:56:21

Prelude

Prelude

Announcements

  • Exam 3 next Friday

Today's topics

  • Vision

How vision informs

  • What's out there?
    • Shape, form, color
  • Where is it?
    • Position, orientation, motion

Electromagnetic (EM) radiation

Features of EM radiation

  • Wavelength/frequency
  • Intensity
  • Location/position of source
  • Reflects off some materials
  • Refracted (bent) moving through other materials

EM radiation provides information across space (and time)

Reflectance spectra differ by surface

Optic array specifies geometry of environment

Color == categories of wavelength

  • Eyes categorize wavelength into relative intensities within wavelength bands
  • RGB ~ Red, Green, Blue
    • Long, medium, short wavelengths
  • Color is a neural/psychological construct

RGB monitors

How a camera works

The biological camera

The biological camera

Parts of the eye

  • Cornea - refraction (2/3 of total)
  • Pupil - light intensity; diameter regulated by Iris.
  • Lens - refraction (remaining 1/3; focus)

Parts of the eye

  • Retina - light detection
    • ~ skin or organ of Corti
  • Pigment epithelium - regenerate photopigment
  • Muscles - move eye, reshape lens, change pupil diameter

Eye forms image on retina

  • Image inverted (up/down)
  • Image reverseed (left/right)
  • Point-to-point map (retinotopic)
  • Binocular and monocular zones

Retinal image

Eyes views overlap

The fovea

The fovea

  • Central 1-2 deg of visual field
  • Aligned with visual axis
  • Retinal ganglion cells pushed aside
  • Highest acuity vision == best for details

Acuity varies across fovea

Acuity varies across fovea

What part of the skin is like the fovea?

Photoreceptors detect light

Photoreceptors detect light

  • Rods
    • ~120 M/eye
    • Mostly in periphery
    • Active in low light conditions
    • One wavelength range

Photorceptors detect light

  • Cones
    • ~5 M/eye
    • Mostly in center
    • 3 wavelength ranges

Photoreceptors "specialize" in particular wavelengths

How photoreceptors work

  • Outer segment
    • Membrane disks
    • Photopigments
  • Inner segment
    • Synaptic terminal
  • Light hyperpolarizes photoreceptor!
    • The dark current

Retina

  • Physiologically backwards
  • Anatomically inside-out

Retina

  • Physiologically backwards
    • Dark current
  • Anatomically inside-out
    • Photoreceptors at back of eye

Retinal layers

Retinal layers

  • Bipolar cells
    • Horizontal cells
  • Retinal ganglion cells
    • Amacrine cells

Next time…

  • From eye to brain